This invention relates in general to vehicle lighting systems. In particular, this invention relates to a method and apparatus for regulating lighting voltage to maintain a relatively constant intensity of light output as an input voltage, such as a vehicle battery voltage, fluctuates during use.
In an effort to conserve energy, light emitting diodes (LEDs) are increasingly being used for vehicle lighting applications. In such applications, power is supplied to the LEDs from a vehicle electrical system, which typically includes a conventional battery. However, it is known that the output voltage of a vehicle battery may vary relatively widely during use, and such variances can have an undesirable effect upon the intensity of the light output from the LEDs. For example, many vehicle manufacturers are developing an engine start/stop mode of operation, in which the vehicle engine is shut off when the vehicle is stationary for more than a predetermined period of time for fuel economy. Upon subsequent cranking the engine for restart, the battery voltage typically experiences a dip, which may undesirably lessen the intensity of light emitted from the vehicle LEDs.
The adverse effects of variations in the battery voltage may be ameliorated by use of a voltage regulating circuit. However, with the increasing number of LEDs being used in vehicles, the current demand upon such a voltage regulating circuit may become excessive, which may lead to overheating and failure. Alternately, an AC/DC switching regulator circuit or a DC/DC regulator circuit may be utilized. However, such circuits are relatively complex and expensive. Therefore, an inexpensive method for regulating the voltage applied to vehicle LEDs as vehicle battery voltage fluctuates would be desirable.